Method and apparatus for forming grooved journals

ABSTRACT

Embodiments of the invention generally provide a method and apparatus for forming grooves on hydrodynamic bearings used with a disc drive. In one embodiment, the invention provides a method and apparatus to align an electrode having a hydrodynamic groove pattern thereon within a journal bearing. The invention provides a floating electrode having groove patterns thereon. The floating electrode is inserted within a hydrodynamic bearing and fluidly aligned to maintain a uniform gap there between.

CROSS-REFERENCE TO A RELATED APPLICATION

[0001] This invention is based on U.S. Provisional Patent ApplicationSerial No. 60/383,949 filed May 28, 2002, entitled “Dynamic MachiningGap For Cylindrical ECM Applications” filed in the name of Dustin AlanCochran. The priority of this provisional application is hereby claimed.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The invention relates generally to the field of disc drives, andmore particularly to an apparatus and method for forming hydrodynamicgrooves in a disc drive.

[0004] 2. Description of the Related Art

[0005] Disc drives are capable of storing large amounts of digital datain a relatively small area. Disc drives store information on one or morerecording media. The recording media conventionally takes the form of acircular storage disc, e.g., media, having a plurality of concentriccircular recording tracks. A typical disc drive has one or more discsfor storing information. This information is written to and read fromthe discs using read/write heads mounted on actuator arms that are movedfrom track to track across surfaces of the discs by an actuatormechanism.

[0006] Generally, the discs are mounted on a spindle that is turned by aspindle motor to pass the surfaces of the discs under the read/writeheads. The spindle motor generally includes a shaft fixed to a baseplate and a hub, to which the spindle is attached, having a sleeve intowhich the shaft is inserted. Permanent magnets attached to the hubinteract with a stator winding on the base plate to rotate the hubrelative to the shaft. In order to facilitate rotation, one or morebearings are usually disposed between the hub and the shaft.

[0007] Over the years, storage density has tended to increase and thesize of the storage system has tended to decrease. This trend has leadto greater precision and lower tolerance in the manufacturing andoperating of magnetic storage discs. For example, to achieve increasedstorage densities the read/write heads must be placed increasingly closeto the surface of the storage disc. This proximity requires that thedisc rotate substantially in a single plane. A slight wobble or run-outin disc rotation can cause the surface of the disc to contact theread/write heads. This is known as a “crash” and can damage theread/write heads and surface of the storage disc resulting in loss ofdata.

[0008] From the foregoing discussion, it can be seen that the bearingassembly which supports the storage disc is of critical importance. Onetypical bearing assembly comprises ball bearings supported between apair of races which allow a hub of a storage disc to rotate relative toa fixed member. However, ball bearing assemblies have many mechanicalproblems such as wear, run-out and manufacturing difficulties. Moreover,resistance to operating shock and vibration is poor because of lowdamping.

[0009] One alternative bearing design is a hydrodynamic bearing. In ahydrodynamic bearing, a lubricating fluid such as air or liquid providesa bearing surface between a fixed member of the housing and a rotatingmember of the disc hub. In addition to air, typical lubricants includeoil or other fluids. Hydrodynamic bearings spread the bearing interfaceover a large surface area in comparison with a ball bearing assembly,which comprises a series of point interfaces. This is desirable becausethe increased bearing surface reduces wobble or run-out between therotating and fixed members. Further, the use of fluid in the interfacearea imparts damping effects to the bearing which helps to reducenon-repeat run out.

[0010] Dynamic pressure-generating grooves (i.e., hydrodynamic grooves)disposed on journals, thrust, and conical hydrodynamic bearings generatelocalized area of high fluid pressure and provide a transport mechanismfor fluid or air to more evenly distribute fluid pressure within thebearing, and between the rotating surfaces. The shape of thehydrodynamic grooves is dependant on the pressure uniformity desired.The quality of the fluid displacement and therefore the pressureuniformity is generally dependant upon the groove depth and dimensionaluniformity. For example, a hydrodynamic groove having a non-uniformdepth may lead to pressure differentials and subsequent prematurehydrodynamic bearing or journal failure.

[0011] As the result of the above problems, electrochemical machining(ECM) of grooves in a hydrodynamic bearing has been developed. Broadlydescribed, ECM is a process of removing material metal without the useof mechanical or thermal energy. Basically, electrical energy iscombined with a chemical to form an etching reaction to remove materialfrom the hydrodynamic bearing to form hydrodynamic grooves thereon. Tocarry out the method, direct current is passed between the work piecewhich serves as an anode and the electrode, which typically carries thepattern to be formed and serves as the cathode, the current being passedthrough a conductive electrolyte which is between the two surfaces. Atthe anode surface, electrons are removed by current flow, and themetallic bonds of the molecular structure at the surface are broken.These atoms go into solution, with the electrolyte as metal ions andform metallic hydroxides. These metallic hydroxide (MOH) molecules arecarried away to be filtered out. However, this process raises the needto accurate and simultaneously place grooves on a surface across a gapwhich must be very accurately measured, as the setting of the gap willdetermine the rate and volume at which the metal ions are carried away.Even in simple structures, this problem can be difficult to solve. Whenthe structure is the interior surface of a conical bearing, the settingof the gap width can be extremely difficult. Manufacturability issuesassociated with conical parts often make it difficult to control thediameter of the cones. Due to mechanical tolerances, the work piece maybe misaligned with the electrode causing an uneven gap and acorrespondingly uneven depth hydrodynamic groove. Therefore, it isalmost impossible to make a tool with fixed electrodes that willguarantee a continued consistent work piece to electrode gap to formdimensionally consistent hydrodynamic grooves.

[0012] Therefore, a need exists for a method and apparatus to provide areliable method and apparatus for forming hydrodynamic grooves that isaccurate and cost effective.

SUMMARY OF THE INVENTION

[0013] Embodiments of the present invention relate to a method andapparatus for electromechanically etching grooves in a surface of aconical bearing. In one embodiment, the invention provides a method foraligning an electrode having one or more hydrodynamic bearing groovepatterns thereon within a hydrodynamic bearing. The method includespositioning the electrode within a hydrodynamic bearing, and providing afluid pressure between the electrode and the hydrodynamic bearing toalign the electrode and the hydrodynamic bearing.

[0014] In another embodiment, the invention provides an apparatus forforming grooves within a hydrodynamic bearing. The apparatus includes afluidstatic bearing configured to support at least a portion of anelectrode having at least one surface carrying a groove pattern toelectrochemically etch on an inner surface of the hydrodynamic bearing.The fluid static bearing utilizes a pressurable medium which maycomprise liquid or air. The apparatus includes a fluid input configuredto couple a fluid flow in a gap between at least some of the electrodeand an inner surface of the hydrodynamic bearing to adjust the width ofthe gap, and a source of electrolyte to be pumped within the gap.

[0015] In another embodiment, the invention provides an apparatus forelectrochemically forming grooves on a hydrodynamic bearing, includingmeans for fluidly supporting an electrode having a groove patternthereon, and means for fluidly aligning the electrode within ahydrodynamic bearing.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] So that the manner in which the above recited embodiments of theinvention are attained and can be understood in detail, a moreparticular description of the invention, briefly summarized above, maybe had by reference to the embodiments thereof which are illustrated inthe appended drawings. It is to be noted, however, that the appendeddrawings illustrate only typical embodiments of this invention and aretherefore not to be considered limiting of its scope, for the inventionmay admit to other equally effective embodiments.

[0017]FIG. 1 depicts a plan view of one embodiment of a disc drive foruse with aspects of the invention.

[0018]FIG. 2 is a vertical sectional depicting one embodiment of a dualconical bearing utilized in the disc drive of FIG. 1 for use withaspects of the invention.

[0019]FIG. 3 depicts a simplified sectional view of an electrochemicalmachining system for use with aspects of the invention.

[0020]FIG. 4 depicts a partial sectional view of an electrochemicalmachining system for use with aspects of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021]FIG. 1 depicts a plan view of one embodiment of a disc drive 10for use with embodiments of the invention. Referring to FIG. 1, the discdrive 10 includes a housing base 12 and a top cover 14. The housing base12 is combined with top cover 14 to form a sealed environment to protectthe internal components from contamination by elements from outside thesealed environment. The base and top cover arrangement shown in FIG. 1is well known in the industry. However, other arrangements of thehousing components have been frequently used, and aspects of theinvention are not limited to the configuration of the disc drivehousing. For example, disc drives have been manufactured using avertical split between two housing members. In such drives, that portionof the housing half which connects to the lower end of the spindle motoris analogous to base 12, while the opposite side of the same housingmember, which is connected to or adjacent the top of the spindle motor,is functionally the same as the top cover 14. Disc drive to furtherincludes a disc pack 16 which is mounted on a hub 202 (See FIG. 2) forrotation on a spindle motor (not shown) by a disc clamp 18. Disc pack 16includes a plurality of individual discs that are mounted forco-rotation about a central axis. Each disc surface has an associatedread/write head 20 which is mounted to disc drive 10 for communicatingwith the disc surface. In the example shown in FIG. 1, read/write heads20 are supported by flexures 22 which are in turn attached to headmounting arms 24 of an actuator body 26. The actuator shown in FIG. 1 isof the type known as a rotary moving coil actuator and includes a voicecoil motor (VCM), shown generally at 28. Voice coil motor 28 rotatesactuator body 26 with its attached read/write heads 20 about a pivotshaft 30 to position read/write heads 20 over a desired data track alonga path 32.

[0022]FIG. 2 is a vertical sectional view of a hub 202 supported by dualconical and journal bearing 200 for rotation about a shaft not shown.The hub 202 is integrated with the sleeve 204. The sleeve 204 includesinternal surfaces 206 having grooved regions 214, 216 forming thehydrodynamic bearing to support the hub during rotation. As iswell-known in this technology, a shaft (not shown) is inserted withinthe sleeve 204 and has dual conical surfaces which face the conicalregions 210, 212 at the upper and lower ends of the journal bearing 200.The shaft would further include a smooth center section which wouldcooperate with a portion of the journal bearing 200 defined by thegrooved regions 214, 216. As is well-known in this field of fluiddynamic bearings, fluid will fill the gap between the stationary shaftand the inner grooved surfaces of the sleeve 204.

[0023] As the sleeve 204 rotates, under the impetus of interactionbetween magnets mounted on an inner surface of the hub 202 whichcooperate with windings supported from the base of the hub 202, pressureis built up in each of the grooved regions 214, 216. In this way, theshaft easily supports the hub 202 for constant high speed rotation.Hydrodynamic grooves 222 on the inner surface of the sleeve 204 caneasily be seen FIG. 2. They include, in one example, two sets of grooves230, 232 for the upper cone and a corresponding set 234, 236 for thelower cone. This particular design also utilizes two journal bearings240, 242 to further stabilize the shaft.

[0024]FIG. 3 is a simplified illustration of a groove forming apparatus300 and method for making hydrodynamic grooves 222. FIG. 2 may bereferenced as needed in the discussion of FIG. 3. For purposes ofclarity, the illustrative apparatus and method are described in terms ofhydrodynamic grooves 222. However, the present invention is not limitedto making this particular combination of hydrodynamic grooves 222. Forexample, the apparatus and method described could be used to make thehydrodynamic grooves (e.g., grooves) 222 inside a single cone or asingle cone cooperating with a single journal bearing or dual conescooperating with one or more journal bearings 200. Further, each of theconical bearings could have one or more sets of hydrodynamic grooves222. The principles of the present invention are applicable in formingany design of conical or journal bearing. The solution provided by thisinvention is especially important in defining conical bearings becausemanufacturability issues associated with conical parts often make itdifficult to control the diameter of the cones. Given this, it isextremely hard to make a tool with fixed electrodes that will guaranteea consistent work piece to electrode gap. As described above, this gapdistance is paramount to the accuracy of hydrodynamic groove dimensions.Considering fluid dynamic bearings, the importance of the accuracy ofhydrodynamic grooves is that a fluid dynamic bearing generally comprisestwo relatively rotating members having juxtaposed surfaces between whicha layer or film or fluid is maintained to form a dynamic cushion with anantifriction medium. To form the dynamic cushion, at least one of thesurfaces, in this case the interior surfaces of sleeve 204, are providedwith the hydrodynamic grooves 222 which induce fluid flow in theinterfacial region and generate a localized region of dynamic highpressure.

[0025] With continuing reference to FIG. 3, groove-forming apparatus 300includes an fluidstatic bearing 306. Fluidstatic bearing 306 includes anair inlet 308 to receive fluid 310 such as pressurized air, clean dryair (CDA), liquid and the like. Internal surfaces 307 of fluidstaticbearing 306 define a longitudinal bore 309. Longitudinal bore 309 insidediameter is sized to hold a floating electrode 302 therein. Floatingelectrode 302 has an outside diameter sized smaller than longitudinalbore 307 to define a gap 316 there between. Fluid flow through inlet 308into gap 316 is at sufficient viscosity or pressure provides force FX1between internal surfaces 307 and floating electrode 302. FX1 is of amagnitude capable of supporting floating electrode 302 to maintain gap316. In this embodiment, pressure within gap 316 between internalsurfaces 307 and floating electrode 302 center and support such floatingelectrode 302 within longitudinal bore 309. Fluidstatic bearing 306 mayinclude one or more end walls not shown to prevent floating electrode306 from moving outside longitudinal bore 309.

[0026] Floating electrode 302 includes an extension 304 extending fromone end thereof. Extension 304 has an outside diameter sized to fitwithin an inside diameter of journal bearing 200 (i.e., work piece) toform a fluid gap 322 there between. The journal bearing 200 is rigidlyheld in place by a clamping apparatus not shown. Extension 304 isconfigured with a hydrodynamic journal pattern 324 juxtaposed to insidesurfaces 206. Hydrodynamic journal pattern 324 may be used to formhydrodynamic grooves 222 on the journal bearing 200, for example. Duringa hydrodynamic groove forming operation, electrolyte 320 is pumpedthrough an electrolyte inlet 321 into fluid gap 322. As electrolyte 320is generally non-compressible, electrolyte 320 fills fluid gap 322centering electrode extension 304 within journal bearing 200. In thisembodiment, electrolyte 320 is used to center the extension 304 withinjournal bearing 200.

[0027] In another aspect of the invention, Floating electrode 302 mayfurther include a fluid delivery bore 315 extending axially therethrough, and at least partially through extension 304. Fluid deliverybore 315 includes a positioning fluid inlet 314 on one end and aplurality of fluid jets 328A-C coupled to an opposite end of fluid bore315. Fluid jets 328A-C are disposed so that positioning fluid 312received from fluid inlet 314 exits at least partially against an insidesurfaces 206 of journal bearing 200. To maximize centering pressure FX2and holding force FY2, fluid jets 328A-C may be angled at an angle αapproximately 45 degrees relative the inside surfaces 206 they contact.Positioning fluid 312 may be any fluid configured to work withelectrolyte 320, and may be an electrolyte similar to or the same aselectrolyte 320.

[0028] As illustrated in FIG. 4, fluid jets 328A-C may be radiallyspaced approximately uniformly about extension 304 so that positioningfluid 312 discharged from fluid jets 328A-C provide uniform centeringforces FX2 and FY2 against the journal bearing 200. Positioning fluid312 exits from fluid gap 322 via an end of journal bearing 200. Duringanother alignment operation of extension 304 within journal bearing 200,positioning fluid 312 is pumped though fluid inlet 314 and forcedthrough fluid jets 328A-C. Fluid forces FX2 and FY2 balance force FX1 inan equilibrium condition so that extension 304 is horizontally andvertically centered within journal bearing 200. While three fluid jets328A-C are illustrated spaced so the angle Θ is approximately 120degrees apart to provide an equal fluid force FX2 to center theextension 304 within the journal bearing 200, any number orconfiguration of fluid jets 328 may be used to provide such centeringand aligning forces.

[0029] The ECM process can then be executed by then applying anelectrical potential to the work piece 200 and floating electrode 302,the work piece receiving the positive potential and the floatingelectrode 302 serving as the cathode and receiving the negativepotential. By timing the current flow, an imprint in the form of thegroove patterns 222 shown in FIG. 2 are placed on the work piece 200. Asis well-known, the width and depth of the resulting hydrodynamic grooves222 is controlled by the duration and level of current applied to thework piece 200 and the floating electrode 302. The current level beingmodified primarily by the fluid gap 322 which has now been adjusted byfluidstatic bearing 306, electrolyte 320, and positing fluid 312 viafluid jets 328A-C.

[0030] While the foregoing is directed to embodiments of the invention,other and further embodiments of the invention may be devised withoutdeparting from the basic scope thereof, and the scope thereof isdetermined by the claims that follow.

1. A method for aligning an electrode having one or more journal bearinggroove patterns thereon within a hydrodynamic bearing, comprising;positioning the electrode within the hydrodynamic bearing; and providinga fluid pressurable medium within a gap formed between the electrode andthe journal bearing to align the electrode and the hydrodynamic bearing,and pressurizing the medium.
 2. The method of claim 1, wherein themedium is a fluid.
 3. The method of claim 1, wherein the mediumcomprises air at pressure to align the electrode.
 4. The method of claim1, wherein providing a medium comprises directing a fluid flow from theelectrode against at least some portion of an inner surface of thejournal bearing, wherein the fluid provides a centering force againstthe inner surface.
 5. The method of claim 1, wherein at least a portionof the electrode comprises fluid jets for directing the fluid flowagainst at least some portion of an inner wall of the journal bearing.6. The method of claim 5, wherein directing the fluid flow provides aforce having a magnitude to form a gap between the electrode and innerwall.
 7. The method of claim 1, wherein positioning comprises providingair flow within a gap formed between at least a portion of the electrodeand an inner surface of an fluidstatic bearing.
 8. The method of claim7, wherein providing air flow comprises adjusting the air flow to alignthe electrode relative an inner bore defined by the fluidstatic bearing.9. An apparatus for forming grooves within a journal bearing,comprising: an fluidstatic bearing configured to support at least aportion of an electrode having at least one surface carrying a groovepattern to electrochemically etch on an inner surface of the journalbearing; a fluid input configured to couple fluid flow within a gapbetween at least some of the electrode and an inner surface of thejournal bearing to adjust the width of the gap; and a source ofelectrolyte to be pumped within the gap.
 10. The apparatus of claim 9,further comprising a power source to energize the electrode, theelectrolyte, and journal bearing.
 11. The apparatus of claim 9, whereinthe fluid input is configured to direct fluid flow from the electrodeagainst at least some of the inner surface of the journal bearing. 12.The apparatus of claim 9, wherein the electrode comprises fluid jetsconfigured to direct a fluid flow against at least some of the innersurface of the journal bearing.
 13. The apparatus of claim 12, whereinthe fluid jets are spaced radially about the electrode at an angleconfigured to provide the fluid flow in a direction to align theelectrode with the inner surface of the journal bearing.
 14. Theapparatus of claim 13, wherein the angle is selected to provide an anglebetween the fluid jets so that the fluid jets are about equally spacedapart.
 15. The apparatus of claim 12, wherein the fluid flow is about 45degrees relative the inner surface.
 16. An apparatus forelectrochemically forming grooves on a journal bearing, comprising:means for fluidly supporting an electrode having a groove patternthereon; and means for fluidly aligning the electrode within a journalbearing.
 17. The apparatus of claim 16, wherein means for fluidlysupporting the electrode comprises an fluidstatic bearing coupled to theelectrode configured to support the electrode within the journalbearing.
 18. The apparatus of claim 16, wherein means for fluidlysupporting the electrode comprises an fluidstatic bearing having an airinput configured to direct air flow against at least some of theelectrode of a magnitude to form a gap between the electrode andfluidstatic bearing.
 19. The apparatus of claim 16, wherein means forfluidly aligning the electrode comprises fluid jets disposed within theelectrode and configured to direct a stream of fluid against an innerwall of the journal bearing.
 20. The apparatus of claim 16, whereinmeans for fluidly aligning the electrode comprises a fluid delivery boreaxially disposed within the electrode, the fluid delivery bore includesfluid jets extending though the electrode and configured to direct astream of fluid against an inner wall of the journal bearing.